Tuesday, December 27, 2011

Cell biology

Cell can be defined as a unit of biological activity delimited by a semi permeable membrane and
capable of self reproduction. Cells are basic structural and functional unit of life.

Discovery of cell:
Janssen (1590): Invented compound microscope.
Robert Hooke (1665): Discovered cell.
Anton Van Leeuwenhoek (1675): First study living cell.

Cell theory
A German botanist Schleiden (1838) and Zoologist Theodor Schwann (1839) found that tissues
were made up of cells. They combined their views and proposed a popular theory called cell
Fundamental features of cell theory are:
1. All organisms are made up of cells.
2. Each cell is made up of a small mass of protoplasm containing one nucleus in its inside
and plasma membrane with or without on its outside.
3. All cells are basically similar in chemical composition and metabolic activity.
4. Function of an organism is the sum total activities and interactions of constituents of
However cell theory does not apply for all organisms. Following are some exceptions are:
1. Bacteria and cyanobacteria lack the true nucleus. Their nuclear mater (DNA) is not
enclosed by nuclear membrane.
2. Plants likes Vaucheria (algae) and Mucor, Rhizopus (Fungi) are exception to the cell
theory because their bodies are made up of the cytoplasm with many nuclei i.e.
3. Viruses are the living organism which lack cellular organisms.
The cellular Totipotency
Totipotency is the ability of living vegetative cell of plant to regenerate into complete plant.
Haberlant (1902), a German botanist, first propose that every living vegetative plant cell should
be able to regenerate a whole plant.

Unicellular organisms
1. The body of organism is made up of a single cell.
2. All the function of the organism is performed by a cell.
3. Cell is generally large in size.
4. The cell possesses power of division.
5. Any injury to the cell may lead to the death of the organism.
Eg: Amoeba, Chlamydomonas, Euglena etc.
Multicellular organism
1. The body is made up of many cells.
2. A cell performs one or few functions. Each cell can’t perform all the activities.
3. Cells are smaller in size.
4. All the cells of the organism do not have power of division.
5. They have great capacity of survival as dead cells are continuously replaced by the new
Eg: Spirogyra, Human beings etc.
Plant cell
1. Cell wall made up of by cellulose.
2. Plastids are present in plant cells.
3. A mature plant cell possesses a large central vacuole.
4. Centriole is absent.
5. Nucleus is pushed to one side in the peripheral cytoplasm by vacuole.
6. Mitochondria are usually fewer.
7. During cell division cytoplasm divides by cell plate formation.
8. Plant cell are capable of forming all the amino acids, co-enzymes and vitamins.
Animal cell
1. The cell wall is absent. The cell is enclosed by a plasma membrane.
2. Plastids are absent in animal cell.
3. Vacuoles are either small or absent.
4. Mitochondria are usually numerous.
5. Cytoplasm division by furrow formation.
6. Animal cells can’t form all the amino acid, co-enzymes and vitamins.
Prokaryotic cell
A cell in which the nuclear (genetic) material is not enclosed by a definite nuclear membrane,
such types of nucleus is called incipient nucleus. Such type of cell is known as prokaryotic cell.
Characteristics of prokaryotic cells
1. They lack nuclear membrane.
2. Important cell organelles like mitochondria, chloroplast, endoplasmic reticulum, golgi
body etc are absent.
3. The size range from 100-2000 nm.
4. Prokaryotic cell are primitive type of cell.
5. Cell wall composed of amino acid and muramic acid.
6. Transcription (DNA? RNA) and translation (DNA?DNA) takes place in cytoplasm.
7. It takes 20-60 min to complete cell cycle.
8. The ribosome found in prokaryotic cell is 70s (50s+30s) types.
9. Respiration occurs by cytoplasmic membranes.
10. Nucleus lacks the nuclear membrane, nucleolus and nucleoplasma.
11. It contain circular double stand DNA.
12. Plasmid is present.
13. Centrioles are absent.

Eukaryotic cell
Eukaryotic cell is well-organized cell, a cell which possesses membrane bound organized
nucleus and other cell organelles is termed as eukaryotic.
Characteristics of eukaryotic cell
1. Nucleus enclosed in nuclear membrane.
2. Genetic material present as more than one chromosome.
3. Endoplasmic reticulum, mitochondria, chloroplast, golgi body etc cell organals are
4. 80s as well as 70s ribosome present in eukaryotic cell.
5. Cell wall usually made up of cellulose (in plant) and chitin (in fungi).
6. Plasmid and pilli are absent.
7. Cell division takes place by mitosis and meiosis cell division. Amitosis cell division takes
place in few organisms such as paramecium, amoeba etc.
8. Transcriptions occur in nucleus and translation takes place in cytoplasm.
9. Cell cycle is long takes 12-24 hours to complete.
10. True vacuoles are present.
11. Centrioles are present.
12. Mitotic spindle is formed in cell division.
13. Size range from 10,000 to 1,00,000 nm.
Examples of eukaryotic cell
All plant and animal cell, ostrich egg, amoeba, R.B.C., W.B.C. etc

Parts of Eukaryotic cells
1. Cell wall
Cell-wall is outermost rigid, protective and semi transparent covering of plant cell and cells of
fungi, bacteria and some Protista. It is totally absent in animal cell. It was discovered by Robert
Hooke in 1665.
Fungi cell wall is made up of Chitin.
Bacteria cell wall is made up of peptidoglycan.
Plant cell wall is made up of cellulose, hemicelluloses, pectin.
The plant cell wall is differentiated into following layers and structure.

1. Middle lamella: it is the outer most cementing layer. It is made up of calcium and
magnesium pectate.
2. Primary wall: it is found inner to middle lamella. Primary wall is made up of pectin and
hemicelluloses. It is more or less elastic nature.
3. Secondary wall: it is thick, rigid and inelastic. It is found to primary wall. It is made up
of cellulose, hemicelluloses, pectin and lignin.
4. Plasmodesmata: primary wall and secondary wall are not formed continuously. They
form gaps called plasmodesmata. It is cytoplasmic bridge between two cells.
In animal protoplasmic bridge is called desmosomes.
Function of cell wall
1. It gives definite shape to the cell due to its rigidity.
2. It protects the protoplasm against mechanical injury.
3. Cell wall of the root hair absorbs water.
4. Cutine and suberin of cell wall of stem and leaves help to reduced rate of transpiration.
5. The nature of cell wall is permeable which allows exchange of any substance through its.
2. Cell coat
The plasma membranes of many Protista and animal cell do not have cell wall, filamentous layer
of oligosaccharides and glycoproteins is found surrounding the plasma membrane. This layer is
further strength by deposition of calcium salt, silicon and other materials, and is called the cell
1. It protects the underlying plasma membrane.
2. It provides shape to the cell.

Cell membrane is thin transparent membrane which encloses cytoplasm of all the living cells.
Cell membrane is also called plasmalemma.
Similar types of membrane are found in the covering of many cell organelles like mitochondria,
chloroplast, endoplasmic reticulum, golgi body etc. The membrane of cell organelles is called
sub-cellular membrane. The sub-cellular membrane and collectively called as biological
membranes or bio-membrane.
Cell membrane is very thin, elastic and living structure. Chemically it is made up of lipid (20-
40%), protein (60-80%) with some carbohydrate about 5%.
Structures of cell membrane have several types; important models are described below.

1. Sandwish model
According to Danielli and Davson, cell membrane consists of 4 layers, 2 layers of
phospholipids and 2 layers of protein. Phospholipid molecules are present between protein
layers so this model is called sandwish model.

2. Fluid mosaic model
This model is widely accepted model proposed by Singer and Nicholson (1972). According
to this model, protein is not found in uniform layer but found in mosaic pattern like icebergs
in sea.

Hydrophobic tail of phospholipid layer lies towards center where as hydrophilic head lies
towards periphery. Glycoprotein and glycolipid are also constituent of cell membrane.
Glycoprotein and glycolipid consist of branch oligosaccharides.
Function of cell membrane
1. Cell membrane protects the cell from injury.
2. The nature of cell membrane is selectively permeable. It allows only selected substances
pass through it.
3. Transportation of materials takes place through plasma membrane by different process
such as diffusion, osmosis etc.
4. It function as receptor site for various stimuli such as hormone, antigen etc.
5. It provides sheath for cilia and flagella.
6. Sub-cellular membrane forms separate chamber for specific metabolism.
Example: mitochondria are site of cellular respiration.

Protoplasm is defined as the physical basic of life. Protoplasm is divided into nucleoplasma and
The chemical composition of protoplasm is as follows.
Water : 70-90%
Protein : 7-20%
Carbohydrate: 1%
Lipids: 2-3%
Inorganic materials: 1%
RNA: 0.7%
DNA: 0.4%
Major elements constituting protoplasm are
Carbon 20%
Oxygen 62%
Hydrogen 10%
Nitrogen 3%
Trace element Ca, P, Cl, S, K, Na, Mg, I, Fe, 5%
Cytoplasm is jelly-like semi-fluid, general mass of protoplasm excluding nucleus including all
other components. Its components include cytoplasmic matrix, cell organelles and cell
Cytoplasmic matrix consists of water, salts of Na, K and other metals.
Cell organelles: cell organelles are living sub-cellular bodies of cytoplasm which have definite
size, shape and specialized for particular function eg: mitochondria, chloroplast, golgi body,
endoplasmic reticulum etc.
Cell inclusions: cell inclusions are non living metabolically inactive substance found in
cytoplasm for example carbohydrate, protein, lipid, pigments. Hormones, tannin etc.
1. It helps in the exchange of materials between organelles.
2. It is the site of synthesis of a number of biochemical molecules such as carbohydrate,
nucleotides, protein and co-enzyme.
3. It is the site of glycolysis and biosynthesis of fatty acid.

It is an active mass movement of cytoplasm around the central vacuole in one direction or around
small vacuoles in several directions.
It is also known as cytoplasmic streaming. This movement of cytoplasm helps in
i. Movement of cell organelles and cell inclusions.
ii. Distribution of materials inside the cell.
iii. Formation of pseudopodia in amoeba.

Gr. Mitos = thread, chondrion= granule
Mitochondria were first of all observed by Kolliker (1880) in muscle of insects. Mitochondria
are commonly called as power house of cell because energy synthesis in the form of ATP during
aerobic respiration. It is the site of cellular respiration.
C6H12O6+ 6O2------------> 6CO2+ 6H2O + 38ATP
Mitochondria are found in all kinds of eukaryotic cell except mammalian RBC and sieve tube
The mitochondria may be rod, filamentous, somewhat spherical, oval, globular, cylindrical,
spiral or cup shape and may change one form to another form depending upon the physiological
conditions of the cells.
Size: size of mitochondria is variable, normally they have 5-10 um in length and 0.6-2.0 um in

Ultra structure

Mitochondria consist of two membranes and two chambers; outer and inner. Outer membrane is
smooth while inner membrane is folded inward to form finger like structure called cristae.
Which increase physiological active area.
Outer chamber is filled with fluid having few enzymes. Inner chamber consists gel like substance
called matrix. Matrix consists of protein, ribosome 70s, double stranded circular naked DNA,
single standed RNA, amino acid, fatty acid etc.
1. They are power house of cell which generates energy in the form of ATP.
2. They help in formation of yolk during ovum formation.
3. Few amino acids such as glutamine acid, aspartic acid are synthesized in mitochondria.
4. They help in elongation of fatty acid.
5. Mitochondria regulate the calcium ion concentration in cell.
6. Mitochondria provide important intermediates for the synthesis of chlorophyll, steroids,
cytochromes etc.
Plastids [2064, 2066]
Plastids are colored organelles of cell. Plastids occur in plant, bacteria, Blue green algae, fungi
(chromatphores instead of plastids).
According to their structure, pigments and functions plastids are divided into 3 types.
1. Chloroplast 2. Chromoplast 3. Leucoplast
1. Chloroplast (Gr. chlors = green , plast = living) [2067]
Chloroplast is commonly called ‘Kitchen of cell’ because food is prepared from CO2 and H2O
during photosynthesis. It is the site of photosynthesis.
Shape: shape is variable biconvex and circular (in mesophyll cell of plant), cup- shaped
(chlamydomonas), star shaped (zygnema), spiral ribbon shaped (spirogyra).
Size: Size is variable, it measure 4-10 um in length and 2-4 um in breath.
Number: number of chloroplast in a cell is variable. Eg: 1 in chlamydomonas. 1 to many in
spirogyra , 20-40 in mesophyll cell.
Ultra structure
Chloroplast is double membranous structure. Both membranes are smooth. Chloroplast consists
of gel like ground substance called as stroma or matrix. In stroma, chlorophyll bearing sac like
structure Called thylakoids or lamella. The group of thylokoids called grana. Each granum has 2-
100 thylakoids. Lamella bears photosynthetic unit called quantasomes. Quantasomea bears 230
chlorophyll molecules. Stroma consist of double stranded circular naked DNA, single standed
RNA, 70s types of ribosomes, starch granules, lipid droplets, enzymes for dark reaction etc.
Photosynthesis takes place in two phases: - light reaction and dark reaction. Light reaction takes
place in granum where as dark reaction takes place in stroma.
fig 7

Function of chloroplast
1. Chloroplast is the site of photosynthesis. Organic compounds are synthesized from
inorganic material.
2. They provide green colour to plant parts.
3. They liberate O2 into the atmosphere which keeps the balance of O2 in atmosphere.
4. They utilize CO2 so help to reduce CO2 concentration in atmosphere which helps to
reduce global warming.
2. Chromoplast ( Gr. Chromo = colour, plast= living)
Chromoplasts are coloured plastids they are yellow or reddish in colour. It is found in petals,
ripe fruits, leaves of some plants etc. they contain caretonoid pigment.
Structure: Chromoplast is similar to chloroplast but lack chlorophyll, grana, intergranal
1. chromoplast provides attractive colour to different plant part.
2. Attractive color of flower help to attract pollinating insects.
3. Attractive colour of fruit helps in dispersal of seed by animals.
4. They are the site of phospholipid synthesis.

Leucoplast (Gr. leuco= white, plast= living)
Plastids without pigment are called leucoplasts. They are found in embryonic cells,
meristamatic cells, root cell etc. grana are absent in leucoplast.
Function: Leucoplast store food material.
Plastids are interchangeable.
One form of plastid can be changed into another form naturally.
Leucoplast? chloroplast ? chromoplast.
(Ovary)    (Unripe fruit) (Ripe fruit)

Mitochondria and chloroplast are semi-autonomous organelles.
Both organelles have own DNA, RNA and 70s types of ribosome. They can manufacture few
necessary proteins themselves, so they are called a semi- autonomous organelles.

Golgi complex (Golgi apparatus)
Occurrence: Golgi complex generally occurs in cytoplasma . It is absent in prokaryotic cell,
sieve tubes of plant, antherozoides of bryophytes and pteridophytes.
Shape: Shape of golgi complex is not fixed.
Size: 2-5um in diameter.
Golgi body is formed by unconnected unit called dictyosomes.
Number: number of golgi body depends upon metabolic activities of cell. Generally a plant cell
consists of 10-20 dictyosomes. It may be 1 in algae to 15,000 in rhizoidal cell of chira.
Structure: Golgi body is made up of 4 kinds of structure cisternae, tubules, vesicles and
golgian vacuoles. Cisternae are flattened sac like unbranched structure which are arranged
parallel. At the end of tubules, small sac like structure is attached called vesicles. Tubules of
maturing surface produce large vesicles called golgian vecuoles.

1. Golgi body involves in collection and secretion of cell products. Collection from convex
surface, secretion from concave surface.
2. It synthesized carbohydrate such as mucilage cellulose etc.
3. It gives rise to primary lysosomes.
4. The production of hormone by endocrine glands is mediated through Golgi apparatus.
Endoplasmic reticulum
Occurrence: The endoplasmic reticulum is present in all the eukaryotic cells except germinal
cells and matured mammalian RBC. It is also absent on prokaryotic cell.
ER is an extensive network of membranes which is formed by 3 types of elements: -
1. Cisternae: cisternae are flattend sac like unbranched structure made up of single
membrane. They are 40-50nm in diameter. They lie parallel to each other. The outer
surface of cistern bears ribosomes.
2. Tubules: they are tube like irregular, branched structure forming net-like system along
with cisternae. They are 50-100nm in diameter.
3. Vesicles: vesicles are rounded or oval membrane structure. They are 25-500nm in

Types: Depending upon the nature of its membrane, ER is divided into 2 types.
a. Smooth endoplasmic reticulum(SER)
b. Rough endoplasmic reticulum (RER)
Smooth endoplasmic reticulum (SER)
It does not bear ribosomes over its membrane.
It mainly consists of tubules and vesicles.
It involves in synthesis of glycogen and lipids.
Rough endoplasmic reticulum (RER)
It bears ribosome over its membrane.
It mainly consists of cisternae and a few tubules.
It involves in synthesis of protein.
1. It gives mechanical support to the cytoplasmic matrix.
2. It help in quick intracellular transportation of materials.
3. It gives rise to cell wall.
4. It involves in synthesis of glycogen, lipid, steroids and proteins.
5. It takes part in detoxification of toxic chemical.
Lysosome is single membrane bounded small vesicles containing hydrolyzing enzyme. They are
the site of cellular digestion and help in intracellular digestion of food. Lysosome involves selfdigestion
of cell by lysosomal enzymes, when after the cell death Lysosomal enzymes are
released, so the lysosome are also called succidal bags.

Occurrence: Lysosomes are present in all animal cell except mammalian RBC and prokaryotic
cell. They are generally rounded but may be irregular.
Size: size of lysosomes varies from 0.2-0.5 um in diameter.
Number: the number of lysosomes in a cell varies with the cell types.
Lysosome is single membranous structure containing hydrolytic enzymes. About 40 different
kind of hydrolytic enzymes are found in Lysosomes. They digest different materials.
For example:
Name of enzyme Substance Product
Proteases Protein Amino acid
Lipase Lipid Giycerol and ftty acid
Nucleases Nucleic acid Nucleotides
Glycosidases Carbohydrate monosaccharides

fig 10

Lysosomes exist in more than one morphological form. This phenomenon is called
polymorphism. Depending upon the content and function, they are divided in to 4 types.
1. Primary lysosomes: it is the newly formed lysosomes from golgi body. Which contain
2. Secondary lysosomes: when primary lysosomes fuse with food vacuole form secondary
3. Residual bodies (Tertiary lysosomes): in secondary lysosomes, food materials are
digested. The digested food materials are diffused into cytoplasm and remaining
undigested food (residue) resides in lysosomes. Lysosome having residue are called
residual bodies.
4. Autophagic vacuoles: when primary lysosomes fuse intercellular organelles form
autophagic vacuoles.
1. Lysosomes take part in intercellular as well as extra cellular food digestion.
2. Lysosomes of WBC destroy foreign proteins, toxic substances and pathogenic microorganisms.
3. Old and useless organelles are also digested by lysosomes.
4. During metamorphosis certain embryonic structure like tail, gills of tadpole are digested
through lysosomes.
Ribosomes are small sub-spherical granular organelles which are not enclosed by membrane.
Ribosome are Called “protein factory of cell” because all types of proteins are synthesized in
Occurrence: Ribosomes are found in all kinds of cells except mammalian RBC.
Structure: Each ribosome is made up of two unequal sub-units. Large sub-unite and smaller
sub-unites. Both sub-unites are made up of ribonucleoprotein particles. At the time of
protein synthesis, many ribosome line up and join an mRNA chain to synthesize copy of
protein such group of ribosome on mRNA is called polyribosome or polysome.
Types: Based on sedimentation coefficient, ribosome divided into 2 types.

a. 70s types: It is found in both prokaryotic cell and eukaryotic cell. Subunits of 70s types
of ribosome are 30s and 50s. It is also called organelle ribosome because it occurs in
mitochondria and chloroplast.
b. 80s types: It is found in eukaryotic cell. Subunits of 80s types of ribosome are 40s and
60s. It is found in cytoplasm so it is called cytoplasmic ribosomes.
1. Ribosomes are the site of protein synthesis. it synthesizes all kinds of proteins.
2. They provide site for the attachment of tRNA and mRNA during protein synthesis.
3. All enzymes and few hormones such as insulin are protein they are produced on
Centrioles are non membranous cell organelles found in animal cell. They are found in
near nucleus. They have ability to replicate. Each centriole is made up of 9(triplet)+0
arrangement of microtubules. It has 9 peripheral group of microtubules and no microtubules in
1. Centrioles form spindle fibre.
2. Centrioles form basal body of cilia and flagella
and control their movement.

Cytoskeletons are supportive frame work inside the cell. They are made up of protein. Two
types of cytoskeletons founds in cells.
a. Microfilaments: microfilaments are ultra microscopic, long. Narrow, thin structure
which occur in eukaryotic cell. It composed of actin and myosin protein.
They maintain the shape of cell.
Cyclosis is caused by the activity of microfilaments.
They are associated with cytokinesis in animal cells.
Actin and myosin are associated with contraction of muscles.
b. Microtubules: Microtubules are unbranched, hollow, cylindrical structures. It is made up
of spirally arranged protein called tubline (a-tubulin and ß-tubulin) protein.
They maintain the shape of cell.
Microtubules are cytoskeleton of cilia and flagella.
They help in movement of nuclei during cell division.
Cilia and flagella
Cilia and flagella are microscopic, hair or thread like motile structures. Cilia are found in ciliated
protozoans( Paramecium) and flagella are found in flagellated protozoans such as Euglena,
Spermatozoa of animals.
Similarities between cilia and flagella.
1. Both are involved in locomotion, feeding and protection.
2. Both are thin, fine hair like movable projections.
3. Both are covered by cell membranes.
Difference between cilia and flagella.
Cilia Flagella
Length is short(5-20nm) Length is large (100-200um)
The number of cilia of the cell is very large
The number of flagella per cell is usually few
Cilia are found in ciliated protozoane eg:
Flagella acre found in flagellated protozoane
eg: Euglena.
They help in locomotion.
They create water current to obtain food from aquatic medium.
Cilia of kidney remove excretory substances.
Cilia of paramecium help in conjugation.
Vacuoles are non-cytoplasmic areas present inside the cytoplasm.
Occurrence: vacuoles are found in all eukaryotic cells. In animals, vacuoles are small in size and
large in number. In plant cells, large size vacuoles are found in small number.
Structures: A vacuole is made up of two parts : tonoplast and cell sap. Tonoplast is the single
membrane of vacuole. It encloses fluids called cell sap. Cell sap consists of minerals, salts,
water, sugar, amino acids, pigments, O2, CO2 and west products.
Types of vacuoles: Sap vacuoles (filled with fluid), Contractile vacuoles (having fresh water),
Food vacuoles (having food), Gas vacuoles (having gas).

1. Vacuoles help in osmoregulation and
2. They store digested or undigested food.
3. They contain water soluble pigments.
4. Waste products such as tannins and latex are
also found in vacuoles.
Microbodies are small cell organelles bounded by a single membrane. They are 3 types.
1. Peroxisomes: they are single membranous vesicles having enzymes catalase peroxidase.
2. Glyoxysomes: they are small vesicles. They contain enzyme for conversion of lipid into
3. Sphareosomes: they are found only in plant cell. They contain hydrolytic enzymes such
as protease, lipase, phosphatase etc. so they are also called plant lysosomes.
Nucleus is important component of cell, contain all the genetic information and control all
cellular metabolisms, so it is called brain of cell.
Shape: The nucleus is generally rounded. It may be oval or elliptical.
Size: The average diameter of nucleus varies between 3um- 25um.
Number: cells usually have one nucleus. The number of nucleus may be two to more in cell of
Rhizopus, Vaucheria, Mucor etc.
Occurrence: Nucleus is found in all eukaryotic cell except mammalian RBC, sieve tube element.
An interphase nucleus consists of 4 different structures:
1. Nucleare membrane: nucleus has two membranes. Space between two membranes is
called perinuclear space. Each membrane is made up of lipoprotein. Outer membrane
bears ribosomes.
2. Nucleo plasma: it is transparent gel like substances found inside nucleus. It contains
nucleoside, nucleotides, enzymes, nucleolus etc.
3. Chromatine reticulum: in nucleoplasma. There are thin, long thread like structures
called chromatin fibres. Chromatine fibres are actually elongated chromosomes.
Chromatine fibres overlap each other to produce a network called chromatine
reticulum. Chromatine have two region:
a. Euchromatin: lightly stained region
b. Heterochromatin: darkely stained region.

4. Nucleolus: nucleolus is membraneless dark spherical body found in nucleoplasma. It
contains nucleoprotein and RNA.
Function of nucleolus:
a. It syntheszes rRNA.
b. It forms ribosome.
c. It is essential for spindle fibre formation.
d. It stores nucleoproteins.
Function of nucleus
1. It controls all the vital activity of cells.
2. It is the site of nucleic acid synthesis.
3. It contains genetic material.
4. Ribosomes are formed in nucleolus of nucleus.
5. Spindle fibres in plants are formed with the help of nucleolus.
Chromosomes (Chroma= colour ,some=body)
Shape: chromosomes are long thin thread like structure.
Size: the size of chromosome varies from 0.5um to 30um in length and 0.2 to 0.3um in diameter.
Number: the number of chromosome is fixed for a particular species but numbers differ from
species to another species. For example: human 2n=46, Onion 2n=16, Maize 2n=20.
(Haplopappus gracilis 2n=2, Ophioglossum reticulatum 2n=1262, Ascaris melanocephala 2n=2,
Autocantha 2n=1600.)
The cell having homologous chromosomes are called diploid cells and represented by 2n.
The cell having no homologous chromosomes are called haploid cells and represented by n.
Structure of chromosomes
The chromosome is defined as the coloured body of nucleus. During metaphase and anaphase of
cell division the chromosome become short and compact bodies having definite shape and size.
Chromosomes are compose of DNA, RNA and protein. The electron microscopic structure of
each chromosomes include the chromonema, centromere, secondary constrictions, telomeres
and satellites.
Types of chromosomes:
On the position of centromere, chromosomes are divided into 4 types.
a. Metacentric: the centromere is situated in the middle and the chromosome has two
equal arms resembling V-shape.
b. Sub-metacentric: the centromere is located slightly away from the center and the
chromosome has two unequal arms resembling L-shape.
c. Acrocentric: the centromere is sub-terminal in position and chromosome appears
rod-like having one smaller arm in comparison with the other.
d. Telocentric: the centromere is located at the tip of the chromosomes; therefore, the
chromosome has only one arm.

Cell inclusions are non-living structure of cytoplasm. They are categorized into 3 types;
1. Reserve food material: Reserve food materials are organic compounds synthesized in
cell and stored up in particular cells and lateral utilized as food. Reserve food materials
found either in soluble or insoluble form. These are three main groups:- carbohydrate,
proteins and lipids.
2. Excretory materials: Excretory materials are by-product of many biochemical reactions.
In plant, amount of excretory material is very high because there is no excretory system.
Some example are:- tannins, resin, essential oil, gums, latex etc
3. Secretary products: Secretary products are chemical compounds which are secreted by
protoplasm in small quantities to perform special functions. Example: - nectar, enzyme,
hormone, vitamins. Pigments etc.

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